inexpensivefully print. and this book is one of the first books that is literally filled with photographs of various kinds of people and various emotional states. and darwin is particularly interested in children. he studied his own children very carefully, was curious about their behavior and it struck him that children expression emotions in a particularly pure and powerful form and here we see approach happiness and sadness in achild. and this, of course, raises the question how do we classify emotion? and darwin implied and we now have ner good reason to believe that we claskifiedthem along two dimensions: valence and intensity. here we have valence. so there are anywhere from six to seven emotions, i illustrate seven here, that range from happiness that is approach, surprise, disgust, contempt, anger, fear, and sadness. moreover, for each of these, there are degrees of intensity.